Technical Field
The present disclosure relates to a Ti—Al-based alloy ingot having ductility at room temperature, and more particularly, to a Ti—Al-based alloy ingot having ductility at room temperature, which has a lamellar structure in which α2 phases and γ phases are arranged subsequently and regularly and has ductility at room temperature in a casting state where the subsequent heat treatment is not performed by controlling a width of the α2 phase, a width of the γ phase and a ratio of α2/γ.
Description of the Related Art
A Ti—Al-based alloy is a kind of intermetallic compounds that have been spotlighted as an advanced light-weight heat-resistant material, and is a two-phase alloy including about 10% of Ti3Al.
An ingot having a two-phase lamellar structure of TiAl(γ)+Ti3Al(α2) is produced by a typical melt solidification method.
Due to superiority in fracture toughness, fatigue strength and creep strength, a lamella structure of the TiAl enables the TiAl to exhibit characteristics useful to be practicalized as a light-weight high-temperature material, but it is difficult for the TiAl to be used as a casting material because of insufficient ductility at room temperature.
Such insufficient ductility is primarily caused by delamination occurring at a lamellar boundary when stress is vertically applied to the boundary.
Accordingly, by reducing sizes of crystal grains and adding beta and gamma phases having relatively excellent ductility as compared with the lamellar structure, there have been efforts to improve strength and ductility of the TiAl as well as high-temperature characteristics.
In the related art for producing the TiAl alloy having a lamellar structure including beta and gamma phases, a Ti—(41˜45)Al—(3˜5)Nb—(Mo,V)—(B,C)-based alloy is used (H. Z. Niu et al., intermetallics 21 (2012) 97 and T. Sawatzky, Y. W. Kim et al., Materials Science Forum, 654-656 (2010) 500)).
Further, U.S. Pat. No. 4,294,615 discloses a technology of improving ductility of a TiAl by adding vanadium (V) to a gamma TiAl matrix, and U.S. Pat. No. 4,842,820 discloses a technology of improving strength and ductility of a TiAl by adding Boron (B).
In addition, U.S. Pat. Nos. 4,842,819 and 4,879,092 disclose a technology of improving ductility of a TiAl by adding chrome (Cr) and a technology of improving ductility and oxidation resistance of a TiAl by simultaneously adding chrome and niobium, respectively.
Disadvantageously, in the aforementioned related arts, since hot processing such as hot forging, rapid solidification, and hot extrusion are performed on the TiAl, it is difficult to simply predict from a result of such hot processing whether or not characteristics of a casting body are improved.
Moreover, since mechanical characteristics are tested through a high-temperature measurement or a bending test is performed, it is difficult to understand tensile properties at room temperature.